Memory scanning to find byte patterns

3 files changed, 92 insertions, 7 deletions

diff --git a/src/main.c b/src/main.c
index e255ec5..ee33aac 100644
--- a/src/main.c
+++ b/src/main.c
@@ -23,9 +23,23 @@ int main(int argc, char *argv[])
   waitpid(pid, NULL, __WALL);
   LOG("Attached to process %d\n", pid);
 
-  /* Do stuff ... */
-  parse_vmmap(pid);
+  char *byte_seq = "secret text";
+  size_t byte_seq_len = strlen(byte_seq);
+  MemscanResult *head = memscan(pid, (uint8_t*)byte_seq, byte_seq_len);
+  MemscanResult *cur = head;
 
+  printf("\n\n\nMemory scan results:\n");
+  printf("%-16s|%-16s|%-10s|%-s\n", "Address", "Base", "Offset", "Name");
+  puts("--------------------------------------------------");
+  while (cur) {
+    printf("%-16p|%-16p|%#-10lx|%-s\n",
+           cur->mapping->begin + cur->offset,
+           cur->mapping->begin,
+           cur->offset,
+           cur->mapping->name);
+    cur = cur->next;
+  }
+  printf("\n\n");
   ptrace(PTRACE_DETACH, pid, NULL, NULL);
   LOG("Detached from process %d\n", pid);
 
diff --git a/src/vm.c b/src/vm.c
index 8e62426..82f67fd 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -3,6 +3,7 @@
 #include <string.h>
 #include <ctype.h>
 #include <stdint.h>
+#include <sys/mman.h>
 #include "vm.h"
 #include "util.h"
 
@@ -45,8 +46,8 @@ VMMapping* parse_vmmap (int pid)
 
     VMMapping *new_mapping = xmalloc(sizeof(VMMapping));
     *new_mapping = (VMMapping) {
-      .begin = begin,
-      .end = end,
+      .begin = (void*)begin,
+      .end = (void*)end,
       .r = perms[0] == 'r',
       .w = perms[1] == 'w',
       .x = perms[2] == 'x',
@@ -63,7 +64,7 @@ VMMapping* parse_vmmap (int pid)
       head = cur = new_mapping;
     }
 
-    LOG("%lx-%lx %c%c%c%c %s\n",
+    LOG("%p-%p %c%c%c%c %s\n",
         cur->begin,
         cur->end,
         cur->r ? 'r' : '-',
@@ -75,3 +76,65 @@ VMMapping* parse_vmmap (int pid)
 
   return head;
 }
+
+static off_t memfind(const uint8_t *hay, size_t hay_size, const uint8_t *needle, size_t needle_size)
+{
+  for (off_t i = 0 ; i < hay_size - needle_size; ++i) {
+    if (memcmp(&hay[i], needle, needle_size) == 0) {
+      return i;
+    }
+  }
+  return hay_size;
+}
+
+MemscanResult* memscan(int pid, uint8_t *byte_seq, uint64_t byte_seq_len)
+{
+  char fmem_path[1024] = {0};
+  sprintf(fmem_path, "/proc/%d/mem", pid);
+  FILE *fmem = fopen(fmem_path, "rb+");
+  VMMapping *vmmaps_head = parse_vmmap(pid);
+  VMMapping *cur_vmmap = vmmaps_head;
+  MemscanResult *cur = NULL, *head = NULL;
+
+  while (cur_vmmap) {
+    if (!cur_vmmap->r) {
+      cur_vmmap = cur_vmmap->next;
+      continue;
+    }
+    LOG("Scanning [%p]\n", cur_vmmap->begin);
+
+    size_t region_size = cur_vmmap->end - cur_vmmap->begin;
+    uint8_t region_data[region_size];
+    fseek(fmem, (off_t)cur_vmmap->begin, SEEK_SET);
+    fread(region_data, 1, region_size, fmem);
+
+    off_t offset = 0;
+    while (offset += memfind(region_data + offset,
+                             region_size - offset,
+                             byte_seq,
+                             byte_seq_len),
+           offset < region_size) {
+      LOG("Matched pattern at [%p]\n", cur_vmmap->begin + (off_t)offset);
+      MemscanResult *new_result = xmalloc(sizeof(MemscanResult));
+      *new_result = (MemscanResult) {
+        .mapping = cur_vmmap,
+        .offset = offset,
+        .next = NULL,
+      };
+
+      if (head) {
+        cur->next = new_result;
+        cur = new_result;
+      }
+      else {
+        head = cur = new_result;
+      }
+
+      offset += byte_seq_len;
+    }
+
+    cur_vmmap = cur_vmmap->next;
+  }
+
+  return head;
+}
diff --git a/src/vm.h b/src/vm.h
index 25849e7..4a994f9 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -3,8 +3,8 @@
 #include <stdint.h>
 
 typedef struct VMMapping {
-  uint64_t begin;
-  uint64_t end;
+  void *begin;
+  void *end;
   uint8_t r:1;
   uint8_t w:1;
   uint8_t x:1;
@@ -14,6 +14,14 @@ typedef struct VMMapping {
   struct VMMapping *next;
 } VMMapping;
 
+typedef struct MemscanResult {
+  VMMapping *mapping;
+  off_t offset;
+  struct MemscanResult *next;
+} MemscanResult;
+
 VMMapping* parse_vmmap (int pid);
 
+MemscanResult* memscan(int pid, uint8_t *byte_seq, uint64_t byte_seq_len);
+
 #endif // _VM_H_